Spatial distribution of intracellular, free Ca2+ in isolated rat parotid acini.
The spatial distribution of intracellular, free Ca2+ ([Ca2+]i) in rat parotid acini was measured by imaging fura-2 fluorescence from individual acinar cells by means of a digital imaging microscope. Upon cholinergic stimulation in a Krebs-Ringer bicarbonate buffer at (37 degrees C), [Ca2+]i increased synchronously at both the basolateral and luminal membranes as well as in all cells of the secretory endpiece, reaching peak [Ca2+]i levels 1 s after stimulation. Atropine addition caused a rapid down-regulation of [Ca2+]i, which, however, never reached prestimulatory levels. When acini were stimulated in a medium containing 5 nM Ca2+, the Ca2+ mobilization arising from internal pools caused an increase in [Ca2+]i predominantly near the basolateral area, where the endoplasmic reticulum is located, and standing Ca2+ gradients were observed for up to 10 s. A mathematical model is developed to simulate the time courses of the Ca2+ profiles through the cytoplasm using estimated values of the Ca2+ diffusion coefficients and the cytosolic Ca2+ buffering capacity. It is concluded that under physiological conditions, the Ca2+ release from the endoplasmic reticulum is responsible for the activation of the basolaterally located K+ channels. Furthermore, Ca2+ influx from the interstitium is responsible for much of the rise in [Ca2+]i near the luminal membranes, where the Cl- channels are supposed to be located.
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Department of General Physiology and Biophysics, University of Copenhagen, Denmark.
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Sten-Knudsen
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D000818:Animals; D002118:Calcium / Q000032:analysis* / Q000378:metabolism / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002412:Cations / Q000494:pharmacology; D002469:Cell Separation; D005455:Fluorescent Antibody Technique; D016257:Fura-2; D007091:Image Processing, Computer-Assisted; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism; D008297:Male; D008433:Mathematics; D008954:Models, Biological; D010306:Parotid Gland / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D002412:Cations; D015221:Potassium Channels; D002217:Carbachol; D002118:Calcium; D016257:Fura-2